This is hidden brain.
I'm Shankar Vedantam.
In 1980, a bomb exploded at the central train station in Bologna, Italy.
85 people were killed.
Hundreds were injured in the wake of the attack, which was later blamed on an italian terrorist organization.
A large clock on the outside of the train station stopped working.
The clock, frozen at 1025, became a symbol of the attack.
The picture of the clock was plastered all over posters and banners during commemorations of the event.
For years afterwards, the clock was quickly repaired.
But in 1990, 616 years after the bombing, city officials permanently stopped the clock at 1025 in remembrance of the tragedy.
In so doing, they unwittingly set up a psychological experiment.
Decades later, when asked whether the clock had ever been fixed, the vast majority of city residents incorrectly reported that it had not.
That included 21 employees of the train station, who presumably saw the clock on a regular basis.
It's not difficult to understand how this error might have come about.
The stopped clock had become an integral element of the story of the bombing.
People's recollections were shaped by the story as much as the facts.
We see the same thing happening in settings large and small.
Two friends might disagree about an incident that took place when they were in school together years before.
Managers and workers may remember different versions of the events that led to a strike, with each group partial to the version that supports its point of view.
When countries go to war, millions of people may collectively remember one chronicle of historical wrongs, while millions of people on the other side of a border remember a completely different set of facts.